Volatile organic compounds (VOCs) are major indoor and outdoor pollutants that can seriously affect human health and ecosystem. In order to ensure the safety of our environment, it is important to be able to measure and control the concentration of such gases with both high selectivity and sensitivity, and at multiple locations. Real-time monitoring of air pollution would be possible by processing data coming from multiple, fast and accurate sensors such as micro gas chromatographs (referred to as “GC” in the following).
Gas chromatography is one of the most popular analytical chemistry tools for the analysis of volatile compounds. This technique consists in detecting peaks corresponding to vapors that are separated upstream in a capillary column usually named chromatography column.
As common pollutants in air are often diluted to very low concentrations (sub-ppb), numerous efforts have been made to enhance the sensitivity of GC systems. This sensitivity is defined through the capability of the column to separate analytes, but also through the minimum concentration that can result in a detection peak that can be resolved from the detector noise. This limit of detection is a key performance parameter that many groups have tried to improve using different types of detectors, such as chemiresistors, micro thermal conductivity detectors or optical micro-interferometers. Another way to improve the sensitivity of a GC system is the use of a preconcentrator. This consists in amplifying the vapors concentration by collecting the analytes on an adsorbent medium during a certain period of time before quickly releasing them in the column, usually through a thermal desorption process. However, the use of this extra component has several drawbacks such as requiring extra power and space, and increasing the measurement time significantly.
Correlation chromatography is a set of techniques that consists in injecting samples according to a pseudo-random binary sequence and getting information from the resulting chromatogram thanks to signal processing. Such techniques have been recently investigated to improve the sensitivity of chromatography devices.
The U.S. Pat. No. 8,297,135 B2 (Trapp) describes a correlation chromatography technique for analyzing multiple samples simultaneously using a unique pseudo-random binary sequence. In this method, analysis is carried out by means of temporal multiplexing: the multiple samples to be analyzed are alternatively injected in “blocks” into a single column thanks to a single injector. A detector placed at an output of the column then acquires the combined signal and after signal processing produces several chromatograms, each chromatogram corresponding to a block of samples.
However a major drawback of the method described in U.S. Pat. No. 8,297,135 B2 is that one sample is injected at a time.
Therefore, the total time required for analyzing the multiple samples increases with the number of samples to be injected.
Besides, such technique produces chromatograms having poor signal-to-noise ratios which lead to inaccurate analysis of the corresponding samples.